During engine operation, combustion gas may leak between the cylinder and its piston rings into the engine crankcase. The leaked combustion gas is referred to as blowby gas and may comprise unburned intake air/fuel mixture, exhaust gas, oil mist, and water vapor.
A positive crankcase ventilation (PCV) system is typically employed to ventilate the crankcase and recirculate the blowby gas to the intake side of the engine for burning the gas in the combustion chamber. The PCV system takes advantage of the negative pressure in the intake to draw the gas out of the crankcase and may utilize a PCV valve to regulate the flow.
A PCV system may be incorporated as a foul air/oil separator in the cam cover of the engine. In the case where design package restraints make it unworkable to package an adequate separator within the cover, the separator may be attached externally to the cover or engine block. An external hose routes the blowby gas to the intake.
In cold environments, a common concern is freezing of the water vapor component of the blowby gas in an external PCV hose and valve. To minimize the risk of freezing, some PCV systems may include a PCV heater, or an extra hot water-carrying hose routed adjacent the PCV hose, or electrically heating or insulating the PCV hose, but these come at a significant cost.
The need exists for a PCV system which is protected from the risk of freezing without adding substantial cost or complexity to the engine.